Nonmagnetic generator ring forgings and steel therefor



ilnited States Patent @fihce 3,055,059 Patented Nov. 20, 1952 3,065,069 NQNMAGNETIQ GENERATOR RING FQRGENGS AND STEEL THEREFQR Elaznnei .i. /ianganello, Wilkins Township, Allegheny County, and Matti H. Pakkala, leasant Hills Borough, Pa, assignors to United States Steel Corporation, a corporation of New Jersey No Drawing. Fiicd July 18, 1960, Ser. No. 43,317 2 iaims. (Cl. 75 -126) This application relates to generator ring forgings and more particularly to generator ring forgings and steels therefor having improved stability and mechanical properties.

The coil supports in rotors of large generators used in the electric power industry are large forgings frequently referred to as generator ring forgings. They commonly range in size from 27 to 63 inches in outside diameter, 19 to 30 inches in length and from 3 to 6 inches in thickness. be nonmagnetic to avoid electrical losses. It is preferred to achieve the high strength required by cold expansion rather than by precipitation or aging. Thus a ductile steel is required. Because of the high losses entailed if a ring ruptures in service, they are rigidly inspected after 25 forming preferably by ultrasonic testing. Since this requires a grain size of ASTM No. 4 or smaller, it is essential that the steel be fine grained.

A commonly used steel for forming generator rings contains about 0.45% carbon, 18% manganese, and 4% 3 chromium. This steel, however, is not completely satisfactory in several respects. The grain size is too coarse, being ASTM No. 3 or coarser, which precludes satisfactory ultrasonic inspection; it has a tendency to precipitate carbides at the grain boundaries if held in the range 35 of 1100 to 1600 R, which is difficult to avoid during forming; and it tends to form brittle magnetic martensite when cold expanded.

We have discovered that the forging defects can be overcome and additional benefits obtained if the composition is modified as follows:

They must withstand high operating stresses and 20 Upon being heat-treated in a similar manner, a conventional steel containing 0.50% carbon, 16.47% manganese, 0.06% nickel, 4.12% chromium, and 0.021% nitrogen exhibited the following mechanical properties:

Table 11 Yield Tensile Elongation Reduction Amount of Cold Strength Strength, in 2", of Area, Working, percent (0.2% Ott p.s.i. percent percent set), p.s.i.

We have discovered also that the temperature in the solution-annealing step influences the grain size. Results of an experiment conducted by solution-annealing samples of Steels A and B at various temperatures were as follows:

Table III ASTM Grain Size Solution Temperature, F.

The steel may contain the usual impurities. Thus it may contain 0.05% maximum phosphorus, 0.02% maximum sulphur, 0.02% maximum aluminum and residual amounts of other elements with the balance iron.

A typical composition of our steel is:

Steel A Steel B C Mn Si Cr N Cb 5% to 6 5 to 6 5 to 6% 4 to 5% 4 t0 6 4% to 5 0. /0 60 17. /19. 50 020/060 4.00/5.00 0.06/0.12 0 25/0.

Thus not only is the steel of this invention inherently at least ASTM #4 in grain size, but the size can be controlled cvcn finer by properly controlling the solution anneal following forging of the rings. i

0 Din P S Si Ni Cr Al N Cb Remainder Compositions of two induction-furnace heats melted and tested are listed below (in percent):

Steel J C Mn Ni Cr N Cb A 0. 47 17. 94 0. 40 4. 68 0. 009 0. 36 B 0. 56 18. 90 O. 48 4. 92 0.11 0.38

Balance substantially iron.

These were heated to 2000 F. for 2 hours and air cooled. The effect on mechanical properties of varying the amount of cold working is shown in the following Table 1:

While we have shown and described several specific embodiments of our invention, it Will be understood that 7 0.06 to 0.12% nitrogen and 0.25 to 0.55% columbium,

balance iron and impurities.

3 4 2. An austenitic steel characterized by good ductility, References Citc in the file of this patent cold workability and a grain size no larger than ASTM UNITED STATES PATENTS #4, said steel containing 0.45 to 0.60% carbon, 17.50 to 19.50% manganese .20 to .60% silicon, 4.00 to 5.00% 2789049 Long et 1957 chromium, 0.06 to 0.12% nitrogen and 0.25 to 0.55% 5 FOREIGN PATENTS columbium, balance iron and impurities. 584 732 Gradt Britain Jan 22 1947 

2. AN AUSTENITIC STEEL CHARACTERIZED BY GOOD DUCTILITY, COLD WORKABILITY AND A GRAIN SIZE NO LARGER THAN ASTM #4, SAID STEEL CONTAINING 0.45 TO 0.60% CARBON, 17.50 TO 19.50% MAGANESE .20 TO .60% SILICON, 4.00 TO 5.00% CHROMIUM, 0.06 TO 0.12% NITROGEN AND 0.25 TO 0.55% COLUMBIUM, BALANCE IRON AND IMPURITIES. 